<template>
  <div class="music-list">
    <div class="back" @click="back">
      <i class="icon-back"></i>
    </div>
    <h1 class="title" v-html="title"></h1>
    <div class="bg-image" :style="bgStyle" ref="bgImage">
      <div class="play-wrapper">
        <div class="play" v-show="songs.length > 0" ref="playBtn">
          <i class="icon-play"></i>
          <span class="text">随机播放全部</span>
        </div>
      </div>
      <div class="filter" ref="filter"></div>
    </div>
    <div class="bg-layer" ref="layer"></div>
    <Scroll @scroll="scroll" :probe-type="probeType" :listen-scroll="listenScroll" :data="songs" class="list" ref="list">
        <div class="song-list-wrapper">
            <Songlist :songs="songs" ></Songlist>
        </div>
        <div class="loading-container" v-show="!songs.length">
          <loading />
        </div>
    </Scroll>
  </div>
</template>

<script type="text/ecmascript-6">
    import Scroll from 'base/scroll/scroll'
    import Songlist from 'base/song-list/song-list'
    import {prefixStyle} from 'common/js/dom'
    import Loading from 'base/loading/loading'

    const RESERVED_HEIGHT = 40
    const transform = prefixStyle('transform')
    const backdrop = prefixStyle('backdrop-filter')

    export default {
        props: {
            bgImage: {
                type: String,
                default: ''
            },
            songs: {
                type: Array,
                default: () => []
            },
            title: {
                type: String,
                default: ''
            }
        },
        data(){
            return {
                scrollY: 0
            }
        },
        methods:{
            scroll(pos){
                this.scrollY = pos.y
            },
            back(){
                this.$router.back()
            }
        },
        watch:{
            scrollY(newVal){
                let zIndex = 0
                let translateY = Math.max(this.minTranslateY, newVal)
                let scale = 1
                let blur = 0
                this.$refs.layer.style[transform    ] = `translate3d(0, ${translateY}px, 0)`
                const percent = Math.abs(newVal / this.imageHeight)
                if (newVal > 0) {
                    scale = 1 + percent
                    zIndex = 10
                }else{
                    blur = Math.min(20*percent, 20)
                }
                this.$refs.filter.style[backdrop] = `blur(${blur}px)`
                if (newVal<this.minTranslateY) {
                    zIndex = 10
                    this.$refs.bgImage.style.paddingTop = 0
                    this.$refs.bgImage.style.height = `${RESERVED_HEIGHT}px`
                    this.$refs.playBtn.style.display = 'none'
                }else{
                    this.$refs.bgImage.style.paddingTop = '70%'
                    this.$refs.bgImage.style.height = 0
                    this.$refs.playBtn.style.display = ''
                }
                this.$refs.bgImage.style.zIndex = zIndex
                this.$refs.bgImage.style.transform = `scale(${scale})`
            }
        },
        computed:{
            bgStyle(){
                return `background-image: url(${this.bgImage})`
            }
        },
        created(){
            this.probeType = 3
            this.listenScroll = true
        },
        mounted(){
            this.imageHeight = this.$refs.bgImage.clientHeight
            this.minTranslateY = -this.imageHeight + RESERVED_HEIGHT
            this.$refs.list.$el.style.top = `${this.$refs.bgImage.clientHeight}px`
        },
        components:{
            Scroll,
            Songlist,
            Loading
        }
    }
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
  @import "~common/stylus/variable"
  @import "~common/stylus/mixin"

  .music-list
    position: fixed
    z-index: 100
    top: 0
    left: 0
    bottom: 0
    right: 0
    background: $color-background
    .back
      position absolute
      top: 0
      left: 6px
      z-index: 50
      .icon-back
        display: block
        padding: 10px
        font-size: $font-size-large-x
        color: $color-theme
    .title
      position: absolute
      top: 0
      left: 10%
      z-index: 40
      width: 80%
      no-wrap()
      text-align: center
      line-height: 40px
      font-size: $font-size-large
      color: $color-text
    .bg-image
      position: relative
      width: 100%
      height: 0
      padding-top: 70%
      transform-origin: top
      background-size: cover
      .play-wrapper
        position: absolute
        bottom: 20px
        z-index: 50
        width: 100%
        .play
          box-sizing: border-box
          width: 135px
          padding: 7px 0
          margin: 0 auto
          text-align: center
          border: 1px solid $color-theme
          color: $color-theme
          border-radius: 100px
          font-size: 0
          .icon-play
            display: inline-block
            vertical-align: middle
            margin-right: 6px
            font-size: $font-size-medium-x
          .text
            display: inline-block
            vertical-align: middle
            font-size: $font-size-small
      .filter
        position: absolute
        top: 0
        left: 0
        width: 100%
        height: 100%
        background: rgba(7, 17, 27, 0.4)
    .bg-layer
      position: relative
      height: 100%
      background: $color-background
    .list
      position: fixed
      top: 0
      bottom: 0
      width: 100%
      background: $color-background
      // overflow-y: auto
      .song-list-wrapper
        padding: 20px 30px
      .loading-container
        position: absolute
        width: 100%
        top: 50%
        transform: translateY(-50%)
</style>
